1. Field of the Invention
The present invention relates to a backlight unit, and more particularly, to a backlight unit and display device having the same, in which an inverter arrangement is modified to prevent problems caused by degradation of heat-radiation capability.
2. Discussion of the Related Art
Generally, a cathode ray tube (CRT), one of various display devices, has been used as a monitor of a measuring equipment, information terminals, or the like as well as television sets. Yet, large size and heavy weight of the CRT fail to meet the demand for compactness and lightweight of electronic products.
There are limitations on the weight and size of the CRT, which is contrary to the trend of compactness and lightweight of various electronic products. Hence, there are various display devices expected to replace the CRT such as LCD (liquid crystal display) using optical electric field effect, PDP (plasma display panel) using gas discharge, ELD (electroluminescent display) using electroluminescence, and the like. Specifically, many efforts to research and develop the LCD are underway.
In order to replace the CRT, the LCD, which is advantageous in compact/slim size, lightweight, low power consumption, and the like, has been widely researched and developed. The LCD has been developed enough to be used in a flat panel display and is adopted as a monitor of a desktop computer, a wide information display device, and the like, as well as laptop computers. Hence, the demand for the LCD keeps rising.
The LCD is mostly a light-receiving device that displays an image by controlling an external incident light, thereby needing a separate light source for applying a light to an LCD panel, i.e., a backlight unit.
Generally, a backlight unit used as a light source of LCD, in which cylindrical fluorescent lamps are arranged, is categorized into an edge-light type and a direct-light type.
First of all, in the edge-light type backlight unit, a lamp unit is provided to one side of a light-guide plate. The lamp unit consists of a lamp emitting light, a lamp holder inserted in both ends of the lamp to protect the lamp, and a lamp reflector enclosing an outer circumference of the lamp to have one side fitted in a lateral side of the light guide plate to reflect the light emitted from the lamp toward the light guide plate.
The edge-light type backlight unit having the lamp unit provided to one side of the light guide plate is mainly applicable to a small-size LCD, such as a laptop computer, a desktop computer, and the like. Hence, the edge-light type backlight unit provides excellent light uniformity, long endurance, and advantage of slimness of LCD.
The direct-light type backlight unit, which has been developed to cope with a wide-screen display over 20 inches, includes a plurality of lamps in one line on a lower side of a diffusing plate to directly illuminate a front side of an LCD panel.
The direct-light type backlight unit has light efficiency higher than that of the edge-light type backlight unit. Thus, the direct-light type backlight has been widely adopted for wide-screen LCDs requiring high brightness.
However, a drive time of the LCD using the direct-light type backlight unit, which is used for a wide-screen monitor, TV set, and the like, is generally longer than that of the LCD for a laptop computer. The number of lamps used in the direct-light type backlight unit is greater than that of the edge-light type backlight unit. Hence, it is highly probable that the lamps of the direct-light type LCD fail to be turned on more easily that those of the edge-light type LCD.
EL (electroluminescence), LED (light-emitting diode), CCFL (cold cathode fluorescent lamp), HCFL (hot cathode fluorescent lamp), EEFL (external electrode fluorescent lamp), or the like can be used as a light source of the edge-light or direct-light type LCD.
A direct-light type backlight unit according to a related art is explained as follows.
FIG. 1 is a perspective diagram of a direct-light type backlight unit according to a related art, and FIG. 2 is a perspective diagram of power drop wires connected to a light-emitting lamp and connector.
Referring to FIG. 1, a direct-light type backlight unit according to a related art consists of a plurality of light-emitting lamps 1, an outer case 3 to support the light-emitting lamps 1, and a plurality of light-diffusion means 5a, 5b, and 5c provided between a liquid crystal display panel (not shown in the drawing) and the light-emitting lamps 1.
The light-diffusion means 5a, 5b, and 5c prevent the shape of the light-emitting lamps 1 from appearing on a display surface of the liquid crystal display panel and provide a light source having a uniform luminosity overall. In order to enhance a light-diffusion effect, a plurality of diffusion sheets and plates are arranged between the liquid crystal display panel and the light-emitting lamps 1.
A reflector 7 is provided to an inside of the outer case 3 to condense the light emitted from the light-emitting lamps 1 on a display part of the liquid crystal display panel. This is to maximize efficiency of light use.
Each of the light-emitting lamps 1, as illustrated in FIG. 1, consists of a cold cathode fluorescent lamp (CCFL). Electrodes 2 and 2a are provided to respective ends of a tube. When power is applied to the electrodes 2 and 2a, the corresponding light-emitting lamp 1 emits light. Respective ends of the light-emitting lamp 1 are fitted in holes formed at both sides of the outer case 3.
Power drop wires 9 and 9a for transferring power for driving the corresponding lamp are connected to the electrodes 2 and 2a of the light-emitting lamp 1, respectively. The power drop wires 9 and 9a are connected to a separate connector 11 to be connected to a driver circuit (not shown). Hence, the connector 11 should be provided to each of the light-emitting lamps 1.
Namely, one power drop wire 9 connected to one electrode 2 of the light-emitting lamp 1 and the other power drop wire 9a connected to the other electrode 2a of the light-emitting lamp 1 are connected to one connector 11 as illustrated in FIG. 2. One of the power drop wires 9 and 9a is bent toward a rear side of the outer case 3 to be connected to the connector 11.
However, in the related art backlight unit of the liquid crystal display device, the connector 11 is connected to the power drop wires 9, 9a of the light-emitting lamp to be connected to the driver circuit (not shown). The connector 11 should be individually provided to each of a plurality of the light-emitting lamps, which can result in complicated wiring. The power drop wires are bent to be connected to the connector 11 to reduce the thickness of the backlight unit, causing reduced work efficiency. Moreover, the wire-bending process should be carried out separately, increasing processing time to lower productivity.
Besides, perforated holes should be provided to the outer case to connect the electrodes to the connector and both of the electrodes should be fitted in the corresponding perforated holes to be externally exposed. Hence, work efficiency is lowered and maintenance and repair of the light-emitting lamps are difficult.
A direct-light type backlight unit according to another related art is explained as follows.
FIG. 3 is a perspective diagram of a direct-light type backlight unit according to another related art, and FIG. 4 illustrates a layout of inverters arranged on a rear side of the direct-light type backlight unit according to another related art.
Referring to FIG. 3, a direct-light type backlight unit according to another related art consists of a plurality of light-emitting lamps 31, each having electrodes 33 and 33a at respective outside ends of a corresponding tube, first and second lower structures 41a and 41b arranged having a distance from each other to fit each length of the light-emitting lamps 31; the first and second lower structures 41a and 41b each having a plurality of recesses 45 at one side to hold both ends of a plurality of the light-emitting lamps 31, respectively; lower supports 91a, 91b, and 91c provided to a space defined between the first and second lower structures 41a and 41b and both sides of the defined space to support the first and second lower structures 41a and 41b; first and second upper structures 43a and 43b provided to leave the same distance between the first and second lower structures 41a and 41b to support the light-emitting lamps 31 together with the first and second lower structures 41a and 41b, the first and second upper structures 43a and 43b having a plurality of recesses 45 corresponding to the recesses of the first and second lower structures 41a and 41b at one sides, respectively; and conductive layers 47a, 47b, 47c, and 47d formed in one direction along the sides of the first and second lower and upper structures 41a, 41b, 43a, and 43b to apply power to the light-emitting lamps 31, respectively.
In order to apply the power to the electrodes at both of the ends of the light-emitting lamps 31, first and second power transform units 50a and 50b are provided to both sides of a rear side of the lower support 91a to have a vertical configuration each. Transformers 51a and 51b are sequentially arranged in a height direction at lower sides on the first and second power transform units 50a and 50b, respectively. Various inverter elements are located on their peripheries.
Generally, at least two light-emitting lamps can be connected to one transformer to be driven. In FIG. 3 and FIG. 4, four light-emitting lamps are connected to one transformer to be driven for example, for which two transformers 51a and another two transformers 51b are provided to both lateral sides of the rear side of the lower support 91a, respectively.
Generally, power transform unit provides current and voltage for a light-emitting lamp drive and converts DC to AC. During such an operation, heat is mostly produced from the transformers 51a and 51b among the inverter elements.
As mentioned in the above description, the transformers 51a and 51b produce most of the heat from the power transform unit. If the transformers are sequentially arranged on the lower side of the power transform unit in a vertical direction, air in the lower side ascends upward by natural convection. The air heated by the heat generating transformers 51a and 51b naturally ascends to heat the inverter elements located on the upper side, thereby extremely lowering the inverter cooling performance.
Moreover, one transformer 51b arranged above the other transformer 51a is more heated by the ascending hot air to raise its temperature higher than that of the other transformer 51a, whereby the corresponding cooling performance is further degraded.
If the current of the light-emitting lamp, which is related to the thermal load of the inverter, is increased, the cooling performance of the inverter becomes worse.
Although not illustrated in the drawing, when a cover shield for inverter protection is further provided, the inverter cooling performance is further degraded by raising temperatures of the inverter elements over the rated temperature, thereby lowering operational reliance of the inverter.